Retrograde neuronal labeling by means of Bisbenzimide and Nuclear Yellow (Hoechst S 769121). Measures to prevent diffusion of the tracers out of retrogradely labeled neurons.

Bisbenzimide and Hoechst S 769121 (Nuclear Yellow, NY), when transported retrogradely through axons to their parent cell bodies, may migrate out of the axons and the cell bodies, as indicated by fluorescence of adjoining glial nuclei. This migration was found to take place both in vivo and in vitro during storage of the sections in water. When using the tracers in 1% concentrations the in vivo migration may be controlled by restricting the survival time. The in vitro migration may be prevented by rapid histological processing of the material.